Wall Street banks will soon have to cough up more details on the private stock markets they run, which are estimated to account for about one-seventh of all U.S. equities trading.

The Securities and Exchange Commission plans to vote Wednesday on rules that would force trading venues known as dark pools to disclose more data and reveal potential conflicts of interest. The SEC proposed the regulations -- some of which resemble requirements for public stock exchanges -- in 2015 after firms including UBS Group AG paid tens of millions of dollars to settle allegations that they allowed practices that benefited high-frequency traders without properly informing other clients.

In the past decade, discussion around dark pools evolved from an obscure market-structure issue to a highly-charged debate over whether traders armed with computer algorithms were using the private venues to take advantage of investors with slower price feeds. The fight gained traction in 2014 after the release of Michael Lewis’s book "Flash Boys.”

Dark pools execute about 14 percent of U.S. equity volume, according to Rosenblatt Securities, an institutional brokerage firm specializing in market structure. Mutual funds and other institutional investors have often used the venues to make big trades because the firms can do so without tipping off the rest of the market.

The SEC’s original proposal required brokerages that operate dark pools to issue public filings that highlight conflicts, spell out how the venues might prioritize certain clients’ trades and disclose trading charges.

While the revised rule that SEC commissioners are scheduled to vote on Wednesday is likely to adhere to the 2015 plan, it will probably take into account more than two dozen comment letters the regulator has received from the finance industry and other interested parties. Morgan Stanley, which runs one of the biggest dark pools, wrote in 2016 that the initial proposal failed to take into account difference between various private venues. Morgan Stanley also said some of the disclosures wouldn’t be helpful to clients.

This article was provided by Bloomberg News.